cold treatment

Cold treatment is the artificial exposure of seeds to sustained low temperatures, usually between 1 and 5 degrees Celsius, for a period of days or weeks. The process mimics the natural winter dormancy that many seeds require before they will germinate in spring. Seeds from temperate climates have evolved to wait out cold months in a dormant state; without experiencing this cold period, they simply will not sprout, no matter how much warmth and moisture you provide.

The treatment works by breaking the seed's dormancy mechanism at the physiological level. During cold exposure, the seed's internal chemistry shifts: growth inhibitor hormones decline, and gibberellins and other germination-promoting compounds accumulate. This period of stratification, as it is technically called, can last anywhere from two weeks for some species to three months or more for others. The seed must remain moist throughout to be effective; dry seeds in cold storage will not undergo the necessary changes.

Common methods and materials

In commercial nurseries and seed operations, cold treatment typically happens in refrigerated chambers at controlled temperature and humidity. For smaller operations, seeds are mixed with moist sand, peat, or vermiculite and placed in plastic bags inside a standard refrigerator. The medium must stay consistently damp but not waterlogged, as fungal rot becomes a risk in wet, cold conditions. Some growers use a damp cloth or paper towel rather than loose medium. The duration depends entirely on species: apple and pear seeds may need 60 to 120 days, while some ornamentals require only 30 days.

Cold treatment is essential for many woody perennials, fruit tree seeds, and herbaceous plants including some wildflowers. Without it, seeds destined for spring planting will remain dormant through the entire growing season. The process is not optional for these species; it is the biological gatekeeper to germination. Improper temperature or duration will result in weak germination rates or complete failure to sprout.

The distinction between cold treatment and dry cold storage is important: stratification requires moisture and active physiological change, whereas simple cool storage just preserves seed viability. Seeds needing cold treatment cannot be kept dry and then planted directly into warm soil expecting quick results. The cold period must be completed first, in wet conditions, before planting into germination media or field beds.